This is the day when Americans in 13 states all go to the polls at once.

And we're going in depth on Super Tuesday coverage in tomorrow's show.

In the meantime, while voters are helping determine

who will appear on the presidential ballot this November,

we cooked up something special for you on CNN Student News.

You know that expression you are what you eat?

Well, CNN has a raw ingredient series.

It looks at how the U. S food industry has changed,

how engineering and importing have replaced old fashioned growing,

and how consumer demands still factors in to how

the industry produces our food.

Christina Alesci has gone inside some of America's biggest food companies,

seeing what most people haven't seen before.

And today we're zooming in on animal feed,

and how what they eat ultimately makes its way to us.

I know I'm not suppose to do it, but every once in a while it's necessary.

Burying my face in the best barbecue I can find.

Americans eat a lot of meat, on average,

up to 126 pounds of poultry, beef, and pork every year.

For some, it's more than their own body weight.

But depending on the animal, producing one pound of meat

can take two, three, or even six pounds of feed.

And what some of our livestock is eating, are things you'd never put in your mouth.

We're going this way.

This is a hog finishing farm in Iowa. It's where pigs get fat.

Over the course of five to six months,

pigs go from about 13 pounds to 270 pounds in this room.

Why did they get all quiet all of a sudden?

They wanna hear what I have to say.

Wow, that's amazing. The smell was awful.

But for me, the most unsavory part of this process

is the one you rarely get to examine closely.

In fact, it's one of the most opaque corners of the meat industry.

It's the animal feed itself.

Most animals raised in this country eat a secret formula.

Some elements of the mix are even unknown to the farmer.

But it's safe to say, that it includes proteins, fats,

and in many cases drugs.

But the base for much of it, is lots and lots of corn

You feel like this is what you were born to do?

I feel this is what God put me on the Earth for.

Roger Zylstra has been farming corn for more than 30 years.

This corn is not corn we'd eat.

No. It's not corn I'd put on my grill. No it is not.

We grow it as a commodity. It really, ultimately comes down to economics.

And if it wasn't for the meat industry,

Roger might have a tough time staying in business.

That's because America's livestock are essentially

just corn conversion machines.

First, the corn travels to a storage facility like this one.

This is one million bushels, or 56 million pounds of corn.

And that's just the overflow from the massive storage containers.

We need to hold a whole year's worth of production at one time.

And then it's metered out throughout the remainder of the year.

Nearly 40 % of all the corn grown in the US goes to animal feed.

Rick Weigel makes hog feed.

How many ingredients are you looking at, at the end of the day?

Probably 10 to 12 different ingredients in.

That includes pig fat. So yes, the pigs are eating pig fat.

One of the biggest feed makers is 250 miles north, Cargill in Minnesota.

We believe our purpose here is to be able to feed a world.

And to feed a world we gotta find the most efficient way

to grow healthy animals. So we spend a lot of time doing

the research to tackle exactly that question.

Cargill says it can get animals just as fat on half the feed,

compared to 40 years ago.

But for many in the industry, it's not just about less feed,

it's about bigger animals.

How do you get livestock to explode in size in just a few months?

The industry has a term for it, renderings.

Animal byproducts like meat and bone meal,

leftover grease from restaurants, and even meal made from poultry feathers.

To get a chicken to market weight, it takes between 42 and 48 days.

I mean that's amazingly fast.

Dr. Keeve Nachman investigates the impact

of industrial food production on public health at Johns Hopkins.

One of his studies found arsenic in chicken meat.

It came from a growth promotion drug in feed

that has since been suspended by the FDA.

In another study, Nachman's team found that some chicken feather meal

contained small amounts of the active drugs in Tylenol, Benadryl, and Prozac.

An industry group rejected the findings, but Nackman stands by it.

No matter how they got there, these feathers are destined for use in animals.

That was surprising and a little troubling to us.

Some producers even use waste,

feeding cows and pigs with what's known as poultry litter

or simply put, chicken poo, which believe it or not

is considered a high protein, lower cost feed.

The FDA proposed banning the practice in 2004

to prevent mad cow disease.

The FDA decided against the regulation,

it said the science simply didn't justify a ban.

The FDA estimates that 1 % of all chicken poop goes into feed.

But none of the farmers I interviewed said they used it.

And there's one more ingredient that's essential to getting growth out of animals.

Where are the drugs? They're in the drug room.

We hand weigh them out and they're dumped in each batch of feed.

Michael says the majority of his customers request antibiotics in their feed.

This is where it comes from.

We asked Keeve Nachman about the drugs we saw in this room.

I did see one drug that has an active ingredient called Carbodox

that has been shown to be carcinogenic,

and cause birth defects, at least in animals.

And that drug has been banned in Canada, in the EU, and in Australia.

It's still approved for use here. But with some restrictions,

which Weigel says he follows closely. And get this,

more than 70 % of all antibiotics sold in the US

are for food production animals.

When I tell people that 75 % of the antibiotics in this country

go into the animal's supply chain, it blows their mind.

It's not possible. How can that be?

It serves the humans, it's just not possible. I mean,

that blows their mind. Jeff Don is trying to reform the food industry

from the inside at Campbell's. Why is that important?

Why should people care about that process?

Because- For those who don't care.

Because clearly there's a sub section of society that does care,

but there's tons of other people that don't care.

All of this cost money. You know, none of this stuff comes free.

And there's a reason that that amount of antibiotics was used by the meat industry.

Because it was effective for them, it was efficient for them.

Ultimately if the low cost food requires us

to do these things to animals and our food system that aren't long- term healthy,

haven't we really simply just externalized that cost on the long- term health issues?

Here's why using so many antibiotics is a problem.

Antibiotics are vital drugs that help defend us from bacteria

that can make us sick or even kill us. But bacteria can evolve.

Every time we use antibiotics, some bacteria survive.

And those drug resistant bacteria can then multiply and spread.

This can result in what many call a superbug.

As we use more and more antibiotics, this problem magnifies.

Generating more kinds of superbugs and making the ones that

already exist even more powerful.

There are already some strains of drug resistant bacteria out there.

And public health officials warn that it'll only get worse

if we don't cool it on the antibiotics.

The FDA says it's changing antibiotic guidelines for animal feed

by December 2016. Veterinarians will have to make sure

the drugs are used judiciously and quote, when

needed for specific animal health purposes.

The feed makers I spoke to said they follow FDA regulations.

But Nachman isn't satisfied with the FDA or the industry.

But is there an alternative? Maybe going organic.

We are farming the same way that my great grandparents would have farmed.

Without drugs, the same pound of meat will cost you more.

The consumers are willing to pay, I think there will continue to be more demand.

And there's the heart of it, demand for cheap meat.

We produce it as efficiently as possible.

And the conditions the animals live in means drugs are often used,

not only to keep them alive, but to make them fat.

Food executive say industrial methods are the only way we're gonna feed

nine billion people in the next three decades.

Maybe, but when you buy an unprocessed raw ingredient,

do you know what's really in it?

Where it's been before it gets to your plate?

And whether it was produced as safely as possible?

Right now, those questions are still too hard to answer.